1. Field of the Invention
This invention relates to the field of mechanical refrigeration and, more particularly, to those refrigeration systems which are equipped with two condensers, located in two different environments. One condenser is generally outdoors, where the heat abstracted by the refrigeration system from the evaporator plus the heat representing the mechanical energy added to the refrigerant vapor in the compressor is dissipated to the atmosphere, or alternately, is dissipated to a stream of water in an evaporative or water-cooled condenser. The second condenser is generally located in some environment which periodically requires heat which would otherwise have to be supplied by burning fossil fuel or by causing electricity to flow through resistance elements. The condenser, which is located in a position where its heat can be utilized, need not be used for heating air. It could be located in the tank of a hot water heater, or wherever the heat rejected by the condenser could be effectively utilized.
2. Description of the Prior Art
The use of two condensers in a mechanical refrigeration system, each located in different environments, is well known. Generally, the design of a system with two condensers is carried out in order to secure some saving in the cost of fuel to heat a space which is reasonably adjacent the space requiring refrigeration. The space requiring heating may be involved in a process requiring the warming of some medium or product, or it might be the warming of a space which must be maintained at a temperature above freezing or a space which must be maintained at a temperature habitable by humans or for some other purpose. By its very nature the space must require less heat than the refrigeration system can provide, either instantaneously or on a year-round basis. If the useful heat sink required more heat than a refrigeration system could provide at every point in time, there would be no need for two condensers. One condenser could be employed, located in the desired zone, and the refrigeration system could pump its heat to that condenser at all times the compresser was in operation. This invention, and the prior art related to it, pertains to the situation where the heating load is at some time less than the heat output which can be generated by the refrigeration system. At some time, the heat generated by the system must be shifted to some sink or environment where its dissipation will not cause any inconvenience or any malfunctioning of the system itself. Having established the need for two condensers, where partial heat reclamation is to be achieved, engineers turned their thoughts in the past to valving systems and controls which would function in a troublefree fashion which would not interfere with normal refrigeration system operation and which, under instruction from some control, would deliver heat first to one condenser, than to the second, alternately.
Since the medium to be controlled was hot refrigerant vapor, the obvious control system required the location of valves, generally automatic, and, most frequently, of the electric solenoid type, in the vapor or hot gas line to each of the condensers These were so arranged that when one opened, the other closed, so that the gas flow from the compressor was to either one condenser or to the other. Selection of condensers was generally determined by a control located in the environment which required or could tolerate the least heat, so that at all times that that environment did not require heat, the heat generated by the system was rejected to the other condenser.
On only the briefest trial of this control arrangement, the refrigeration engineers discovered that the inoperative condenser with its inlet closed quickly filled with liquid refrigerant through its outlet connection. The result was that substantial amounts of refrigerant had to be added to the system sufficient to fill the inoperative condenser. If the two condensers were not of the same size, then enough refrigerant had to be added to the system to fill the larger of the two.
Refrigeration engineers considered the need for the addition of substantial quantities of extra refrigerant a disadvantage. In an effort to reduce the amount of this extra refrigerant required, or eliminate the extra portion of refrigerant entirely, they provided a check valve at the outlet of each of the two condenser circuits. Their logic was that the extra valve would, during the period a condenser was inoperative, prevent the inoperative condenser from filling with liquid refrigerant. These innovators were blessed with initial success, because, on changeover from heat rejection in one condenser to heat rejection in the other, the inoperative condenser was isolated by the closing of its inlet control solenoid valve and the simultaneous closing of its outlet check valve. The glow of success of these innovators, however, was short-lived. Although some check valves and solenoid valves are absolutely bubble-tight, that is, do not allow the adverse flow of any amount of vapor at all over substantial periods of time, most refrigeration valves are not so thoroughly leak-tight and do allow the flow of small quantities of refrigerant through their closed ports to the extent of an ounce or more of refrigerant flow per hour. Where the mode of operation requires one condenser to be operative for long periods, for instance, 4 to 6 months, and the other condenser to be operative for equally long periods, it is easy to see that the valves used to isolate the inoperative circuit must have an unusually high barrier against leakage; otherwise, leakage rates of even a few ounces a day would allow the entire refrigerant charge to migrate into the unused condenser, causing a shortage of refrigerant in the refrigerating section of the system, with the resultant lack of refrigeration. To cope with this problem, the resourceful refrigeration engineers developed a series of curative measures. They either vented the unused circuit to the low side, so that all of the refrigerant contained in it and all the refrigerant that might conceivably leak into it at some future time was drained away in vapor form and vented to the low side, or, alternately, through the use of a time clock, they caused the control valve of the unused circuit to open periodically, for instance, once every 6 hours or once every 24 hours, so that any refrigerant which had been accumulated in it would be pushed out into the main refrigerating circuit and only the residual minimum operating charge would be left in it. Both of these corrective measures have been widely utilized. The timer system is favored by some engineers because it does not add any refrigerant control valves to the system. The evacuation technique is favored by other refrigeration engineers because the inoperative circuit is completely purged of refrigerant and its internal pressure is reduced to that of the low side.